In the related-art, a process cartridge method is adopted for an image forming apparatus using the electrophotographic image forming process. With the process cartridge method, a cartridge can be attached to and removed from an apparatus main body of the image forming apparatus. In this process cartridge method, an electrophotographic photosensitive drum and process devices that perform operations on the electrophotographic photosensitive drum are integrally assembled into a cartridge. Thus, maintenance of the image forming apparatus can be simplified and performed by a user himself or herself.
However, with the image forming apparatus using such a process cartridge method, not only a cartridge having functions matching the image forming apparatus but also a cartridge not having functions matching the image forming apparatus may be attached. As a structure for addressing this problem, the following method has been proposed: that is, when a cartridge not matching to an image forming apparatus main body is inserted, a cam portion for opening/closing a shutter is brought into engagement with a wrong-cartridge-insertion block engagement portion at an opening of the apparatus main body so as to open a shutter, thereby blocking insertion of a wrong cartridge (for example, PTL 1)